With a donation of $970 million, the Facebook co-founder tops the list of the nation's 50 most generous donors. Combined, they gave away $7.7 billion.

While many a social networker enjoys complaining about Facebook ads and timeline changes, a Silicon Valley nonprofit is singing the praises of the online service — and especially its co-founder, Mark Zuckerberg. Last December, Zuckerberg and his wife, Priscilla Chan, donated a whopping 18 million shares of Facebook stock valued at more than $970 million to the Silicon Valley Community Foundation, transforming it into one of the biggest foundations in the country.

The donation was the largest charitable gift on public record in 2013, making Zuckerberg and Chan the country’s most generous philanthropists for the year, according to the annual ranking of 50 published by The Chronicle of Philanthropy. They are the youngest donors to ever make the top of the list.

Altogether, the nation’s top 50 donors gave a combined $7.7 billion to charitable causes last year, up 4 percent from the year before. In addition, another $1.9 billion in pledges was made. It was a good year for charities.

"It's a sure sign that the economy is getting better and people are getting a lot less cautious," said Palmer.

Number two on the list was Texas energy tycoon George Mitchell, a hydraulic-fracturing pioneer who left around $750 million to his family foundation when he died in July. The foundation works to support conservation and sustainability.

In third place was Nike Chairman Philip Knight and his wife, Penelope, who challenged the Oregon Health & Science University Foundation for cancer research to match a $500 million grant in the next two years; if they can’t match it, they don’t get a dime.

Former New York Mayor Michael Bloomberg was number four after giving a total of $452 million to a number of groups focusing on arts, education, environment, public health and other causes.

Notably missing from the list are some of the country’s familiar philanthropists like Bill and Melinda Gates, Ted Turner, and Warren Buffett. But not for lack of generosity; they were paying off hefty pledges from previous years, so although they still gave handsomely, the donation were already accounted for.

And what did it take to get on the list? Coming in at number 50 was Millicent Atkins, a 93-year-old farmer and landowner who bequeathed $37.5 million among three institutions.

Forty-two of the top 50 made gifts of $50 million or more, and the median gift of $86.1 million set a record. The money pledged in 2013 was almost equal to the money donated in the previous two years combined.

The report notes that last year’s stock-market increase was behind the generous giving, but a philanthropic executive at U.S. Trust, Claire Costello, also thinks that family wealth being passed on to the next generation is surging and that charities can expect a surplus of big gifts in 2014 and beyond.